The relationships between tracheal index and lung volume parameters in mild-to-moderate COPD

Although elongated morphological changes in the trachea are known to be related to lung function in chronic obstructive pulmonary disease (COPD), whether the tracheal morphological changes are associated with airflow limitations or overinflation of the lung in the early stages of COPD has not yet been determined. Thus, our aim was to investigate the association of tracheal index (TI) with lung function parameters, including lung volume parameters, in COPD patients with mild-to-moderate airflow limitations.

A retrospective study was conducted in 193 COPD patients with GOLD grades 1-2 (post-bronchodilator forced expiratory volume in 1s [FEV1] ≥ 50% predicted with FEV1/forced vital capacity ratio ≤ 70%; age range, 40-81) and 193 age- and gender-matched subjects with normal lung function as a control group (age range, 40-82). Two independent observers measured TI at three anatomical levels on chest radiographs and CT scans.

Compared with the control group, TI was reduced significantly and "saber-sheath trachea" was observed more frequently in COPD patients. Patients with GOLD grade 2 disease had a lower TI than those with GOLD grade 1. TI had apparent inverse correlations with total lung capacity, functional residual capacity, and residual volume, regardless of the anatomical level of the trachea. Even after adjustments for covariates, this association persisted.

TI is reduced even in mild-to-moderate COPD patients, and TI measured on chest CT shows significant inverse relationships with all lung volume parameters assessed, suggesting that tracheal morphology may change during the early stages of COPD.